Lowest number of camera pictures needed to clear Merry Gear Solid with Big Beard ranking?

Solution 1:

Turns out it can be done with a total of four camera uses, or three with one gun shot, for the Big Beard ranking.

First use in the room where you find the gun
Second use on the 8th floor, to stun the group surrounding the hallways (before the treeline)
Use the gun (or the camera) on the guard near the stairs after going around the treeline
Third use on the ninth floor as seen here